Floppy drive pin 2 question?

Tony Duell ard at p850ug1.demon.co.uk
Mon Mar 14 17:13:13 CST 2005

> I have tried to research the issue further but can I find no authoritative 
> references to pin 2 being anything but an RPM select line.
> Other websites like mine do claim it is use for write current but provide no 
> references to show it.

The IBM PC/AT Options and Adapters Techref supplement (what a title!) 
contains a section on the 'High Capacity Diskette Drive'. It defines pin2 
as '-Reduced write' (the leading '-' meaning active low) and devines it 
as 'The inactive state of this signal indicates that high-density media 
is present requiring normal write currents, and the active state 
indicates low-density media is present, requiring a reduced write current.'

The schematics only show the logic board, not the spindle motor, but I 
can fiond no speed-control connection to the spindle motor on the 
diagram. I can find a circuit connected to pin 2 of the interface 
connector that will control the write current.

I have no evidence that this was ever used in a production drive, of 
course, but there is a document that supports that pin 2 is used to 
control the write current.


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